Once-through boiler with suspended tube system

ABSTRACT

In a once-through boiler having vaporizer heating surface members, in the form of a tightly welded helical winding of tubes, suspended on unheated downcomer tubes, the helical winding of tubes is fixedly connected only at upper and lower ends thereof to the downcomer tubes, while it is connected slidingly to the downcomer tubes at locations intermediate the fixed connections.

' United States Patent 1 1 Bruckner et al.

1111 3,744,458 July 10, 1973 ONCE-THROUGH BOILER WITH SUSPENDED TUBE SYSTEM Inventors: Hermann Bruckner; Werner Emsperger, both of Erlangen, Germany Kraitwerk Union Aktiengesellschaft, Mulheim (Ruhr), Germany Filed: July 8, 1971 Appl. N0.: 165,820

Assignec:

[30] Foreign Application Priority Data July 11, 1970 Germany P 20 34 464.3

US. Cl 122/6 A, 122/235 A, 122/510 Int. Cl. .1 F221) 37/24 Field ofSearch 122/6 A, 235 A, 494,

References Cited UNITED STATES-PATENTS 4/1964 Da /is 122 10 FOREIGN PATENTS OR APPLICATIONS 1,036,332 3/1963 Great Britain 122/6 A 1,414,782 9/1965 France. [22/6 A Primary Examirierl(enneth W. Sprague Assistant Examiner.lames C. Yeung Attorney-Curt M. Avery. Herbert L. Lerner et al.

[57] ABSTRACT In a once-through boiler having vaporizer heating surface members, in the form of a tightly welded helical winding of tubes, suspended on unheated downcomer tubes, the helical winding of tubes is fixedly connected only at upper and lower ends thereof to the downcomer tubes, while it is connected slidingly to the downcomer tubes at locations intermediate the fixed connections.

6 Claims, 2 Drawing Figures ONCE-THROUGH BOILER WITH SUSPENDED TUBE SYSTEM The invention relates to once-through boiler of high output with a vaporizer system winding upwardly around the combustion chamber of the boiler, the vaporizer system being formed of a helical winding of tightly welded-together fin tubes or finned tubes which simultaneously form part of the combustion or fire chamber wall.

It has been known heretofore to suspend the vaporizer system of such a once-through boiler on vertical tubes downwardly traversed by working medium that is below boiling temperature. Such downcomer tubes conduct the working medium coming from an economizer heating surface to the vaporizer heating surface.

The downcomer or supporting tubes, on which the mutually welded helical winding is suspended, are cooled by the water flowing downwardly therein. Heating of the water in the downcomer tubes should be avoided as a matter of expediency because, otherwise, the downward flow of the medium might be hindered therebyand instabilities in the flow might tend to occur. Furthermore, the downcomer tubes ought not to become too heated, becausev otherwise very great changes in the length thereof would have to be taken into consideration. Accordingly, the supporting downcomer tubes are located outside'and adjacent the fire or combustion chamber wall and are shielded, at least in the vicinity of the helical winding, by the tubes of the vaporizer. I

Since the supporting downcomer tubes are colder than the tube wall of the combustion chamber, the different thermal expansions of the supporting downcomer tubes and the helical winding of tubes forming the combustion chamber wall must be taken into consideration. Moreover, different local temperature differences occur.

It is accordingly an object of the invention to provide once-through boiler with suspended tube system wherein the combustion chamber wall and the support tubes are not welded together at locations along the entire length thereof, so as to avoid the occurrence of thermal stresses corresponding to the local temperature difference between the combustion chamber tube wall and the support tubes.

With the foregoing and other objects in view, there is provided, in. accordance with the invention, oncethrough steam boiler comprising a combustion chamber, a vaporizer system formed of a helical winding of tubes welded tightly to one another and extending around the combustion chamber, vertically extending support tube means located adjacent the vaporizer system, the support tube means being downwardly traversible by working medium having a temperature below boiling and means for suspending the vaporizer system from the support tube means, the suspending means comprising respective means located at an upper and a lower part of the helical winding of tubes for fixedly connecting the latter to the support tube means, and a plurality of means located intermediate the respective fixedly connecting means for slidingly'connecting the helical winding of tubes to the support tube means. The fixed connections are force-locking or are welds.

The vertical support tubes are disposed about the entire periphery of the combustion chamber and, in accordance with the invention, is provided with a given prestressing. In the alternative, the helical winding of mutually welded tubes is prestressed. The prestressing may be effected, for example, by applying weight loads or screw connections. By means of this prestressing, the stresses caused by the temperature differences can be suitably counteracted.

In accordance with other features of the invention, the support tubes are distributed in pairs or individually in suitable spaced relationship, forexample, l to 2m, about. the periphery of the combustion chamber so as to providethe necessary supporting capability. When the support tubes are employed in pairs, they can be welded together either along the entire lengths thereof or only at given locations along the lengths thereof so that the helical winding of tubes can be braced at the thus strengthened location-through vertical slide connections. The advantage derived therefrom is that the point of attack of the forces can be located in the neutral fiber of the support tube and thereby avoid moments.

The location at which the support tubes are fixedly or force-lockingly connected to the helical winding of tubes at the lower part of the latter is in the vicinity of the upper edge of the combustion chamber funnel, in accordance with a further feature of the invention. Since the support tubes have a lower temperature, during operation of the once-through boiler, than the temperature of the helical winding of tubes, the tubes of the helical winding are increasingly pressed together when the boiler starts operating. This means that a greater part of the weight of the helical winding of tubes is supported in the lower part thereof, for example at the beginning of the combustion chamber funnel, so that a release of tension occurs in the upper part of the helical winding of tubes. How strongly this tension release takes effect during operation of the boiler de pends upon what prestress was applied; weights of several tons, for example, being able to be suspended.

When such a boiler system is filled for the first time with water at, for example, 150 C, before the furnace has yet been ignited, the temperature of the support tubes is initially higher than that of the mutually welded helical winding of tubes. The prestress applied in cold condition accordingly changes. Due to the large iron mass of the economizer, heating of the feed water proceeds very slowly so that there is only a slight initial temperature drop from the support tubes to the helical winding of tubes when the cold boiler is filled with hot water.

Other features which are considered as characteristic for the invention are set forth in the appended claims.

Although the invention is illustrated and described herein as embodied in'once-through boiler with suspended tube system, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.

The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawing, in which:

FIG. 1 is a sectional view of part of a combustion or fire chamber wall of a once-through boiler with suspended tube system constructed in accordance with the invention; and

FIG. 2 is an enlarged elevational view, partly broken away, of FIG. 1, as seen from the left-hand side of the latter.

Referring now to the figures of the drawing, there is shown a part 1 of a combustion or fire chamber wall which is formed of a helical winding of vaporizing tubes welded together. The vaporizing tubes wind upwardly along the wall of the combustion chamber either only on a single wall or on several walls. The vaporizing tubes I extend horizontally along one or more of the other walls. When such a tube system is suspended, the

weight of such a boiler member per se presents an unduly high load and tensile stress in the region at which it is suspended. Attempts have therefor been often made to provide measures for relieving the tension. It would, moreover, also be sensible to fasten such a boiler member only at the lower end thereof because the weight of the iron mass lying thereabove would again have a deforming effect upon the lower part of the tube wall 1. Attempts have therefor been made to call upon separate support members, especially support members 2 which are upwardly traversed by working medium for suspending the tube wall 1 therefrom.

As shown in FIG. 2, supporting tubes 2 are formed pairwise of tubes 3 and 4 which are directly welded to one another or are welded to one another through the use of intermediate members such as the members 5 to 8. The intermediate members, such as the members 5, 6 and 8, are given dimensions respectively for a single point of attachment, however, it is also possible to employ longer strips 7 as intermediate members so as to be able to effect fastening of the tubes at several loca tions thereof.

As is especially apparent from FIG. 1, in accordance with the invention, only two rigid or fixed connections are provided between the helically wound tubes forming the part 1 of the combustion chamber wall and the support tubes 2, namely, an upper rigid fastening point 9 in the vicinity of the upper end of the vaporizer 1 and a lower rigid fastening point 10 'at the lower end of the vaporizer 1 or at the upper end of the ash hopper or funnel ll of the combustion chamber.

To distribute the loads in the tube wall 1 of the combustion chamber, the prestressing thereof, which is applied before the welding of the lower fixed fastening point to the supporting tubes 2 or the tube wall 1, is of considerable importance. As mentioned hereinbefore, a weight load of several tons can be provided. The combustion chamber wall and the supporting tubes 2 then act, in operational warm condition of the boiler, as a system of two springs coupled to one another, which absorb forces in accordance with their rigidities. In contrast to relieving the weight with constant suspension means,.such construction is simpler and less costly. The ash that is produced distributs itself on the tube wall 1 and the support structure 2 in accordance with their rigidities.

The reinforcing or stiffening structure 22 can be suspended from the supporting tubes 2. Since small relative expansion between the tube wall 1 of the combustion chamber and the reinforcing structure accordingly occur, the edge connections of a horizontal reinforcing support can be of especially simple construction. Besides both fixed attachment points 9 and 10, only a slight connection is provided between the tube wall 1 of the combustion chamber and the supporting tubes 2 at the locations 12 to 18. By suitable clamping, the stability of shape or non-deformability of the tube wall 1 of the combustion chamber can be assured with adequate movability of the structural members. As may be readily seen from FIGS. 1 and 2, an intermediate member, such as one of the intermediate members 5 and 8, is provided at the upper and lower ends of the tube wall 1. A circular hole is formed in the intermediate members 5 and 8 through which a clamping bolt is inserted for rigidly securing the tube wall 1 to the supporting tubes 2. On the other hand, the intermediate members 6 and 7, for example, by-which the supporting tubes 3 and 4 are welded together between the uppermost and lowermost intermediate members 5 and 8, are each provided with elongated bolts 19 and 20, 21 respectively, through which one of the bolts or similar fasteners 12 to 17 are inserted so as to slidingly connect the tube wall 1 to the supporting tubes 2. Thus, whereas the tube wall 1 is rigidly held at the intermediate members 5 and 8 of FIG. 2, it is displaceable vertically along the slots 19, 20 and 21 of the intermediate members 6 and 7, for example.

We claim:

1. A once-through steam boiler comprising a combustion chamber, a vaporizer system including a helical winding of tubes welded tightly to one another and extending around said. combustion chamber, vertically extending support tube means located adjacent said vaporizer system, said support tube means beingdownwardly traversible by working medium having a temperature below boiling, and means for suspending said vaporizer system from said support tube means, said suspending means comprising respective means located at an upper and a lower part of said helical winding of tubes for fixedly. connecting, said upper part and said lower part of said helical winding of tubes to an upper part and lower part respectively of said support tube means, and a plurality of means located intermediate said respective fixedly connecting means for slidingly connecting said helical winding of tubes to said support tube means.

2. Once-through steam boiler according to claim 1 wherein the suspending means located at the lower part of said helical winding of tubes connects the latter force-lockingly with said support tube means, and wherein said combustion chamber has a funnel-shaped bottom, said helical winding tubes being fixedly connected at said lower part thereof to said support tube means in vicinity of the upper edge of said funnelshaped bottom of said combustion chamber.

3. Once-through steam boiler according to claim 1 wherein said support tube means have the properties of a prestressed construction.

4. Once-through steam boiler according to claim 1 wherein said helical winding of tubes have the properties of a prestressed construction.

5. Once-through steam boiler according to claim 1 wherein said support tube means comprises a plurality of tubes secured in pairs to one another, said support tube pairs being spaced apart from each other around the periphery of said combustion chamber.

6. Once-through steam boiler according to claim 1 including reinforcing structure for said combustion chamber located outside said combustion chamber, said reinforcing structure being suspended from said support tube means. 

1. A once-through steam boiler comprising a combustion chamber, a vaporizer system including a helical winding of tubes welded tightly to one another and extending around said combustion chamber, vertically extending support tube means located adjacent said vaporizer system, said support tube means being downwardly traversible by working medium having a temperature below boiling, and means for suspending said vaporizer system from said support tube means, said suspending means comprising respective means located at an upper and a lower part of said helical winding of tubes for fixedly connecting, said upper part and said lower part of said helical winding of tubes to an upper part and lower part respectively of said support tube means, and a plurality of means located intermediate said respective fixedly connecting means for slidingly connecting said helical winding of tubes to said support tube means.
 2. Once-through steam boiler according to claim 1 wherein the suspending means located at the lower part of said helical winding of tubes connects the latter force-lockingly with said support tube means, and wherein said combustion chamber has a funnel-shaped bottom, said helical winding tubes being fixedly connected at said lower part thereof to said support tube means in vicinity of the upper edge of said funnel-shaped bottom of said combustion chamber.
 3. Once-through steam boiler according to claim 1 wherein said support tube means have the properties of a prestressed construction.
 4. Once-through steam boiler according to claim 1 wherein said helical winding of tubes have the properties of a prestressed construction.
 5. Once-through steam boiler according to claim 1 wherein said support tube means comprises a plurality of tubes secured in pairs to one another, said support tube pairs being spaced apart from each other around the periphery of said combustion chamber.
 6. Once-through steam boiler according to claim 1 including reinforcing structure for said combustion chamber located outside said combustion chamber, said reinforcing structure being suspended from said support tube means. 